1. Field of the Invention
This invention relates to an optical disc drive device comprising an optical unit and a movable pickup in which the optical unit is fixedly provided on a chassis and has a light source for radiating a light beam towards an optical disc and a light receiving section for receiving a return light beam reflected from the optical disc, the movable pickup is supported on the chassis for movement along the radius of the optical disc and has an object lens for converging the light beam radiated from the light source to the surface of the optical disc and driving means for driving the object lens at least in a direction along its optical axis. More particularly, it relates to an optical disc drive device in which dust and dirt or the like foreign matter may be prevented from being deposited on the light incident-light outgoing sections of the optical unit and the movable pickup to assure protection of the light incident-light outgoing sections.
2. Description of the Prior Art
An optical disc apparatus is provided in a known manner with an optical pickup device for reproducing information signals recorded on the optical disc or recording information signals on the optical disc.
The optical pickup device includes an optical unit, provided with a light source, such as a semiconductor laser, radiating a light beam to the optical disc, and a light receiving section, such as photodetector(s), for receiving the light beam reflected from the optical disc, and an object lens unit, provided with an object lens for converging the light beam radiated from the light source to the disc surface and a lens driving section for driving and displacing the object lens at least along the optical axis of the object lens.
A conventional optical pickup is constituted by an optical unit provided with a light source and a photodetector(s) and an object lens nit formed as one with the optical unit. The optical unit and the object lens unit are moved in their entirely along the radius of the optical disc by a pickup drive and a recording track(s) of the optical disc is tracked y an optical beam for reading out information signals recorded on the optical disc or recording information signals on the optical disc.
With the above described optical disc drive device employing the optical pickup device, in which the optical unit is constituted as one with the object lens unit, the optical unit and the object lens unit need to be displaced in their entirety, so that the optical pickup device needs to be moved through a larger distance, while the pickup drive is increased in size. Consequently, it becomes extremely difficult to reduce the size of the optical disc drive.
An optical disc drive has been proposed in which the optical unit and the object lens unit are constituted independently of each other and the optical unit is fixedly provided on a chassis provided within the main body of the disc drive device while only the movable pickup including the object lens is supported on the chassis for movement along the radius of the optical disc.
With the optical disc drive device in which the optical unit is provided in this manner, separately from the movable pickup device, the light beam exiting from the light source provided in the optical unit is transmitted through the optical disc drive device via the light incident and exiting section and deflected in its proceeding direction by a reflecting mirror or the like so as to be incident on the object lens via the light incident and exiting section provided in the movable pickup device. The light beam is then converged by the object lens so that the converged light is radiated to a signal recording region of the optical disc. The return light beam, reflected from the optical disc, is incident on the optical unit via an optical path which is the reverse of the light path followed by the above-mentioned light beam incident on the optical disc, and is detected by the light receiving section provided in the optical unit.
Meanwhile, with the above-described optical disc drive in which the optical unit is provided separately from the movable pickup device, since the light beam is transmitted through the light path in the optical disc drive device between the optical unit and the movable pickup device, the optical unit and the movable pickup device are provided with respective light beam incident and exiting sections. That is, with the optical pickup device in which the optical unit is formed as one with the object lens unit, only the object lens is laid open to outside, whereas, with the optical disc drive in which the optical unit is provided separately from the movable pickup device, not only the object lens provided in the movable pickup section but also the light beam incident and exiting sections, provided in the optical unit and in the movable pickup device, is laid open to outside.
If dust and dirt or the like foreign matter is deposited on the light beam incident and exiting section, the light beam undergoes irregular reflection, so that the amount of the light beam transmitted through the optical unit and the movable pickup device is decreased. The result is that a sufficient amount of the light beam cannot be radiated to the signal recording region of the optical disc, while the amount of the return light beam reflected from the optical disc is decreased. Thus the readout signal, obtained by detecting the return light beam at the light receiving section, is collapsed in waveform to render it impossible to reproduce information signals with optimum playback characteristics.
On the other hand, with an optical disc drive device in which a rewritable magneto-optical disc is used as a recording medium, since the amount of the light beam transmitted through the optical unit and the movable pickup device is decreased in this manner, the light beam is radiated on the signal recording region of the magneto-optical disc with only an insufficient power to produce troubles in writing the information signals.